Electrophotographic printing apparatus with repellent bands on the photoconductive member and the developing roller to prevent buildup of toner therebetween

Abstract

An electrophotographic printing apparatus includes a liquid development unit for developing a latent electrostatic image formed on a photoconductive member with liquid developer. The liquid development unit has a developer roller whose surface faces the photoconductive member with a small gap spacing. A pair of spacer films are provided between the developer roller and photoconductive member at positions corresponding to axially end portions of the developer roller to determine the gap spacing. A pair of repellent band members are formed on the surfaces of the developer roller at positions between a developing area and the portion contacting the spacer film. A pair of repellent band members are also formed on the surface of the photoconductive member at positions corresponding to the repellent band member of the developer roller. The pairs of repellent band members prevent the accumulation of the liquid developer and further prevent the closing of the small gap spacing between the surface of the image forming area and developing area.

What is claimed is: 
     
       1. An electrophotographic printing apparatus comprising: a photoconductive member including a surface having an image forming area and a non-image forming area;   means for forming an electrostatic image on said image forming area of said photoconductive member;   a developer roller for developing said electrostatic image with a liquid developer, said developer roller including a surface facing said surface of said photoconductive member, said surface of said developer roller having a developing area facing said image forming area and a non-developing area facing said non-image forming area;   a spacer member for determining a gap between said surface of said photoconductive member and said surface of said developer roller, said spacer member being in contact with both said non-image forming area of said photoconductive member and said non-developing area of said developer roller; and   a first repellent member provided on said surface of said developer roller at a position between said developing area and the portion contacting said spacer member in said non-developing area.   
     
     
       2. An electrophotographic printing apparatus as claimed in claim 1, further comprising a second repellent member provided on said surface of said photoconductive member at a position facing said first repellent member. 
     
     
       3. An electrophotographic printing apparatus as claimed in claim 1, wherein said first repellent member is a coating of fluorine resin on said surface of said developer roller. 
     
     
       4. An electrophotographic printing apparatus comprising: a photoconductive member including a surface having an image forming area and a non-image forming area;   means for forming an electrostatic image on said image forming area of said photoconductive member;   a developer roller for developing said electrostatic image with a liquid developer said developer roller including a surface facing to said surface of said photoconductive member, said surface of said developer roller having a developing area facing said image forming area and a non-developing area facing said non-image forming area;   a spacer member for determining a gap between said surface of said photoconductive member and said surface of said developer roller, said spacer member being in contact with both said non-image forming area of said photoconductive member and said non-developing area of said developer roller; and   a first repellent member provided on said surface of said photoconductive member at a position between said image forming area and the portion contacting said spacer member in said non-image forming area.   
     
     
       5. An electrophotographic printing apparatus as claimed in claim 4, further comprising a second repellent member provided on said surface of said developer roller at a position facing said first repellent member. 
     
     
       6. An electrophotographic printing apparatus as claimed in claim 4, wherein said first repellent member is a coating of fluorine resin formed on said surface of said photoconductive member. 
     
     
       7. A liquid development unit comprising: a container for storing liquid developer;   a developer roller rotatably provided on said container and extending partially into said container, said developer roller including a cylindrical surface having a developing area in its axially central portion and non-developing areas at its axial end portions;   a pair of spacer films provided on said end portions so as to be in contact with said non-developing areas; and   a pair of repellent bands circumferentially provided on said cylindrical surface of said developer roller at positions between said developing area and the portions contacting said spacer films in said non-developing area.   
     
     
       8. A liquid development unit as claimed in claim 7, wherein said repellent bands are coatings of fluorine resin formed on said cylindrical surface. 
     
     
       9. A developer roller for a development unit of an electrophotographic printing apparatus, comprising a cylindrical surface having a developing area in its axially central portion and non-developing areas at its axial end portions, each of said non-developing areas having a cylindrical contacting portion provided on the respective axial ends of said developer roller in contact with a spacer member, and a pair of repellent bands circumferentially provided on said cylindrical surface at positions between said developing area and said cylindrical contacting portions in the respective non-developing areas. 
     
     
       10. The developer roller as claimed in claim 9, wherein said repellent bands are coatings of fluorine resin. 
     
     
       11. A photoconductive member of an electrophotographic printing apparatus, comprising a surface having an image forming area and non-image forming areas at both end portions with respect to a direction perpendicular to a moving direction of said photoconductive member, each of said non-image forming areas having a contacting portion provided on the respective edges of said photoconductive member in contact with a spacer member, and a pair of repellent bands provided on said surface at positions between said image forming area and said contacting portions in said non-image forming areas. 
     
     
       12. The photoconductive member as claimed in claim 11, wherein said repellent bands are coatings of fluorine resin. 
     
     
       13. A method of forming a developer roller for a development unit of an electrophotographic printing apparatus, comprising the steps of: providing said roller with a substantially cylindrical outer surface having a developing area in its axially central portion and non-developing areas at its axial end portions, each of said non-developing areas having a cylindrical contacting portion provided on the respective axial ends of said developer roller in contact with a spacer member, and forming a pair of repellent bands on said cylindrical surface at positions between said developing area and said cylindrical contacting portions in said non-developing areas. 
     
     
       14. A method of forming a photoconductive member for an electrophotographic printing apparatus, comprising the steps of: providing a drum having a photoconductive outer surface, said outer surface having an image forming area and non-image forming areas at both end portions with respect to a direction perpendicular to a moving direction of said photoconductive member, each of said non-image forming areas having a contacting portion provided on the respective edges of said photoconductive member in contact with a spacer member, and forming a pair of repellent bands on said outer surface at positions between said image forming area and said contacting portions in said non-image forming areas. 
     
     
       15. The method of claim 13 wherein said step of forming a pair of repellent bands includes the step of coating said cylindrical surface with fluorine resin, at the locations for said repellent bands. 
     
     
       16. The method of claim 14 wherein said step of forming a pair of repellent bands includes the step of coating said outer surface with fluorine resin at the locations for said repellent bands.